Advanced Mobile Phone Service: Cell-Site Hardware

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<ul><li><p>Copyright 1979 American Telephone and Telegraph Company T H E BELL SYSTEM TECHNICAL JOURNAL </p><p>Vol. 58, No. 1, January 1979 Printed in USA. </p><p>Advanced Mobile Phone Service: </p><p>Cell-Site Hardware </p><p>By N. EHRLICH. R. E. FISHER, and T. K. WINGARD </p><p>(Manuscript received August 1, 1978) </p><p>The hardware facilities of the AMPS cell site connect the mobile radio customer to the land telephone network and perform actions necessary for R F radiation, reception, and distribution; voice and data communications and processing; equipment testing, control, and reconfiguration; and call setup, supervision, and termination. Cell-site operational control is achieved partially through wired logic and partially through programmable controllers. This paper describes the cell-site functional groups, their physical characteristics and design, and the ways they interface with the rest of the AMPS system. </p><p>I. INTRODUCTION </p><p>In the A M P S system, the interface between the land te lephone network and the radio pa ths to the mobiles occurs a t the cell sites. In addit ion to performing functions needed for t runk terrnination and for radio t ransmission and reception, the cell site handles many semiau-tonomous functions under the general direction of the Mobile Telephone Switching Office (MTSO ) . Figure 1 is a block diagram of the major A M P S subsystems. </p><p>Cell sites have facilities to: ( i ) Provide R F radiation, reception, and distribution. </p><p>( ii ) Provide da ta communicat ions with the M T S O and mobiles. (Hi) Locate mobiles. (iv) Perform remotely ordered equ ipment testing. (v) Perform equ ipment control and reconfiguration functions. </p><p>(vi) Perform voice-processing functions. (vii) Perform call setup, call supervision, and call terminat ion </p><p>functions. </p><p>153 </p></li><li><p> MTSO I PROCESSOR </p><p>S W I T C H I N G N E T W O R K </p><p>L . </p><p>R C V </p><p>R C V </p><p>I </p><p>O A T A T E R M I N A L </p><p>V O I C E T R U N K S </p><p>L I N E S U P E R V I S I O N </p><p>F R A M E </p><p>D A T A L I N K S </p><p>CELL SITE " I </p><p>I D A T A F R A M E ~ ~ | </p><p>C O N T R O L L E R I </p><p>D A T A A N O L O C A T I N G </p><p>R A D I O S </p><p>M A I N T E N A N C E A N O T E S T </p><p>F R A M E </p><p>R A D I O F R A M E 0 </p><p>I X M T ^ </p><p>R A O I O F R A M E I </p><p>R A D I O F R A M E 2 </p><p>T T LF' </p><p>R C V ^ </p><p>C O N T R O L L O G I C U N I T U N I T </p><p>T R A N S C E I V E R </p><p>MOBILE ~1 </p><p>I </p><p>J Fig. 1 A M P S major subsystems. </p><p>(viii) Handoff or receive from ano the r cell site any mobile which has moved out of the normal service area of the cell site carrying the call. </p><p>Cell-site operat ions are controlled part ial ly by wired logic and partially by programmable controllers. Control functions a re r edundan t and can be reconfigured as needed to overcome a localized failure. A ba t te ry p lan t assures main tenance of service in case of commercial power outage. Facilities dependen t upon traffic requi rements in each cell coverage a rea a re modular so t h a t addit ional uni ts may be installed as needed to m a t c h busy-hour traffic levels. Th i s will ensure t h a t plant inves tment can grow sensibly as a function of ant icipated revenues. </p><p>154 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1979 </p></li><li><p>Figure 2 is an isometric view of a typical cell site with a capacity of 48 voice channels . T h e precise n u m b e r of frames at each site is a function of the voice channel requi rements for t ha t site. T h e r e are four frame codes, and the smallest size cell site requires one of each code. E a c h radio frame h a s a max imum capacity of 16 radios. When the n u m b e r of voice radios grows beyond 16, ano ther radio frame mus t be added. Each line supervision frame (LSF) can handle 48 voice channels and, when this n u m b e r is exceeded, ano ther L S F is added. A single da ta frame (DF ) and a single main tenance test frame (MTF ) a re necessary regardless of the n u m b e r of voice radios in t h e cell site. T h e max imum size of a cell site is 144 voice radios, which would require a total of 14 frames: nine radio frames, th ree line supervision frames, one da ta frame, and one main tenance test frame.* T h e discussion in this paper of the functional design of the cell site parallels the organization of these frames. </p><p>Sect ion II describes the da ta frame, which serves as the mas ter control center for the cell site. Section III describes the line supervision frame, which interfaces the four-wire voice t runks (originating a t the M T S O ) with the cell-site voice-radio transceivers. Section IV describes the radio frame, which is composed of two bays. Section V describes the main tenance and test frame, which gives the cell site the abi l i tythrough the use of ano ther p rogrammable controllerto test for t roubles in the radio and audio equipment . Section VI describes the power system. Section VII describes the physical design of a cell site. </p><p>II. DATA FRAME </p><p>T h e da ta frame (see Figs. 3 and 4) contains the equ ipment for major cell-site control functions, which include communicat ion with the M T S O , control of voice and da ta communicat ion with mobiles, and communicat ion with the controller in t h e main tenance test frame. Communica t ion between controllers is necessary for request ing performance of specific tes ts and for receiving results. T h e D F contains bo th hardwired logic and programmable controllers. Only one set of hardwired logic and one controller is needed per cell site regardless of the n u m b e r of voice radios. Because of the critical functions performed in the D F , r edundancy of all subassemblies is provided to assure cont inuat ion of service in the presence of a failure. T h e D F can reconfigure itself under the direction of the M T S O , which mainta ins service by permit t ing any malfunctioning subassembly to be replaced with an off-line r edundan t unit. </p><p>T h e da ta frame (see Fig. 4) contains five major subsystems: </p><p>* In addition to these transmission and control frames, four additional W E 111A power system frames and an associated battery system are required for the maximum size cell site. </p><p>CELL-SITE HARDWARE 155 </p></li><li><p>156 THE BELL SYSTEM TECHNICAL JOURNAL. JANUARY 1979 </p></li><li><p>s </p><p>a -Sf </p><p>CELL-SITE HARDWARE 157 </p></li><li><p>T O LSF C O N T R O L L E R </p><p>T O M T F C O N T R O L L E R </p><p>M T S O </p><p>D A T A L I N K A D A T A D A T A </p><p>SET SET A C O N T R O L L E R </p><p>C O N T R O L L E R </p><p>0 </p><p>D A T A L I N K D A T A </p><p>r . </p><p>D A T A S E T SE T </p><p>1 </p><p>C O N T R O L L E R </p><p>C O N T R O L L E R </p><p>1 </p><p>S E T U P R A D I O S </p><p>T O R A D I O F R A M E A N D A N T E N N A S </p><p>N T E R F A C E L O C A T I N G </p><p>R E C E I V E R S </p><p>F R O M A N T E N N A S </p><p>. V O I C E O A T A R E C E I V E R S </p><p>F R O M A N T E N N A S </p><p> T O LSF T O M T F </p><p>C O N T R O L L E R C O N T R O L L E R </p><p>Fig. 4Data frame block diagram. </p><p>( i ) Land da ta Links, described in Section 2.1. ( i i ) Controllers described in Section 2.2. </p><p>(Hi) S e t u p radio communicat ion, described in Section 2.3. (iv) Locating radios, described in Section 2.4. (v) Voice-channel da ta communicat ions, described in Section 2.5. </p><p>2.1 Land data links </p><p>D a t a communicat ion between the M T S O and each cell site takes place over two redundan t da ta links connecting Western Electric 201D da t a sets a t each terminat ion. T h e 201D da ta set operates a t a 2.4-k b / s ra te and supplies T T L level ou tpu ts so t ha t no buffering is required between it and the D F logic. T h e da ta set controller converts the 32-bi t serial messages into 16-bit parallel words for transfer to the controllers. T h e 201D also can configure itself for loop-around testing unde r remote control of the M T S O . Th i s feature is essential for maintenance because t h e cell si tes will normally be unmanned . T h e da ta sets and t h e da t a set interfaces also opera te in t h e reverse direction to t ake and t ransmi t da ta from the controllers to t h e M T S O . </p><p>2.2 Controllers </p><p>T h e controller of the da ta frame (see Fig. 5) consists of a P R O C O N , a writable s tore uni t (wsu) , a par i ty generator and checker, and a da ta bus to connect the P R O C O N to the numerous peripherals with which it mus t communicate . All uni ts are provided redundant ly to assure cont inuat ion of service in the presence of failure. </p><p>T h e P R O C O N is a small general-purpose programmable controller, </p><p>158 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1979 </p></li><li><p>W R I T A B L E S T O R E U N I T O </p><p>I N P U T BUS M U L T I P L E X E R </p><p>P E R I P H E R A L 0 </p><p>LT I N P U T B U S </p><p>M U L T I P L E X E R P R O C O N I </p><p>P E R I P H E R A L I </p><p>P E R I P H E R A L </p><p>W R I T A B L E S T O R E U N I T I </p><p>Fig. 5Data frame controller. </p><p>developed a t Bell Laboratories, designed to have sequencing and control functions with very high reliability. I t is self-checking; an A S W (all seems well) signal indicates the presence or absence of a failure. T h e r edundan t P R O C O N recognizes this indication and repor ts failure to the M T S O . T h e M T S O will then use the properly functioning P R O C O N for further cell-site control and will pr int ou t in a maintenance center a reques t to dispatch a craftsperson to t h e cell site to correct t he problem. </p><p>P R O C O N processes 16-bit parallel da ta words bu t uses 24-bit words for program instructions. I t contains da ta manipulat ion uni ts ( D M U ) , a control uni t (cu-16), and program storage uni ts ( P S U ) . T h e D M U contains instruction decoders, internal registers, logical /ar i thmetic capability, and peripheral communicat ion logic. T h e control uni t contains program-addressing logic, clock distribution, and fault-detection circuits. Each P S U board contains 2048 (2K) 24-bit words of read-only memory (ROM ) . T h e P R O C O N contains 4000 words of R O M and accesses an addit ional 4000 24-bit words of random-access memory (RAM ) in its associated w s u . Th i s increases its effective program store capacity to 8000 words. T h e w s u also provides 2000 18-bit words of da ta memory ( D M ) for P R O C O N access. Sixteen bits of each D M word contain da ta , and t h e remaining two bits are used for pari ty. </p><p>T h e P R O C O N ou tpu t is linked to a 16-bit da ta bus, which connects it to all peripherals, both within the D P and in o ther cell-site frames. </p><p>CELL-SITE HARDWARE 159 </p></li><li><p>Separa te control signals from the P R O C O N indicate the address of the peripheral to be connected to t h e da ta bus to receive a part icular message. In a similar manner , per ipherals are connected to the da ta bus to allow the controller to read information from a peripheral 's ou tpu t register when the peripheral is act ing as a sensor. Par i ty is added a t the source for all da ta messages placed on the bus and is checked by the uni t receiving the message before it is used. </p><p>2.3 Setup radio communication </p><p>Se tup radios, as described in Ref. 1, t ransmi t only data, and are used in t h e initial phase of "set t ing u p " t h e call prior to the es tabl ishment of a voice p a t h for communicat ion. T h e y are for the general (shared) use of the cell site in communicat ing with all mobiles within its zone. In addit ion, the se tup radios also t ransmi t overhead messages to assure t h a t idle mobiles within the cell coverage zone are ready and able to communica te should a call be init iated to or from t h e mobile. </p><p>In the forward direction (land to mobile), referred to as the forward se tup channel , messages may be ei ther one or two words in length. Each word consists of da ta bi ts t ransmi t ted serially a t a ra te of 10 k b / s and encoded before transmission to provide 28 message bits and 12 B C H error detect ion/correct ion bits for a to ta l of 40 bits per word. In t h e reverse se tup direction, the mobile t ransmi tsat the same da ta rate48-bit words, with 36 of these bits available for message informat ion and 12 bits used for the error detect ion/correct ion code. T h e words in the reverse direction vary in number . T h e n u m b e r of words needed is t r ansmi t ted as par t of the message information. In each direction, each word is repeated five t imes to allow a majority voting of t h e detected word to protect the integrity of the transmission against t h e effects of noise, mul t ipa th fading, and interference. T o minimize t h e effects of noise t h a t comes in bursts , t he five repeats of each message in t h e forward direction are interleaved with similar messages addressed to ano ther mobile. Th i s group of two words, each t ransmitted five t imes, is preceded by 10 bits of dot t ing (al ternate ones and zeros) for bit synchronization and 11 bits of Barker Code* for word synchronizat ion (see Fig. 6). T h e bit-and-word synchronization permits the mobiles to frame t h e forward se tup messages and determines when each word and each sequence of t h e five-word repea ts begin and end. Each mobile will look a t only one of the two interleaved sets of words in t h e message s t ream, depending on whe ther the last digit of t h e mobile 's te lephone number is odd or even. </p><p>An addit ional bit, called the busy-idle bit, is inserted immediately following t h e bit sync, the word sync, and every 10 bits of each message word. If t he bit is a 1, t he reverse se tup channel of the part icular cell </p><p>* Barker Code consists of a bit sequence that is highly unlikely to be reproduced by rhythmic or random noise. It is 11100010010. </p><p>160 THE BELL SYSTEM TECHNICAL JOURNAL. JANUARY 1979 </p></li><li><p>(NOT TO SCALEI </p><p>10 11 40 40 40 40 40 </p><p>BIT SYNC WORD SYNCIIWO A, wo a , WO A 2 WO B 2 WD A , </p><p>til III II </p><p>40 40 40 10 </p><p>WO B, WD Aj WD B s | BIT SYNC </p><p>1 lint BUSY-IDLE BIT INSERTION (10 MESSAGE BITS BETWEEN SUCCESSIVE BUSY-IDLE BITS) </p><p>LOGIC 0 BUSY LOGIC I = IOLE </p><p>A, FIRST OF FIVE REPEATS OF WORD A (40-BIT MESSAGE WORD) </p><p>B, * FIRST OF FIVE REPEATS OF WORD (40-BIT MESSAGE WOROI </p><p>Aj SECOND OF FIVE REPEATS OF WORD A (40-BIT MESSAGE WORDI </p><p>B 2 = SECOND OF FIVE REPEATS OF WORD (40-BIT MESSAGE WORD) </p><p>B 5 FIFTH OF FIVE REPEATS DF WORD 8 (40-BIT MESSAGE WORD) </p><p>Fig. 6Forward set-up channel message stream. A given logic unit reads only one of the two interleaved messages. </p><p>site t ransmit t ing the message s t ream is idle, and any mobile desiring to init iate a call or to respond to a page m a y t ransmit . If t he bit is a 0, t h e reverse se tup channel is being used by another mobile t ransmit t ing a call origination or a page response. A mobile wishing to t ransmi t on t h a t channel mus t wait a shor t t ime interval and moni tor the channel again unti l idle bits are observed. </p><p>T h e r e is no essential difference between a voice radio and a se tup radio, per se. In fact, the identical radio equipment codes may be used in ei ther position. T h e differences in practice between the se tup radio and the voice radio are the frequency channel to which each is assigned and the interface circuits t h a t control the operat ion of t h e radio. </p><p>In the case of the se tup radio t ransmit ter , four circuit packs,* three designated as se tup t ransmi t te r interface and one as setup t ransmi t te r controller, t ak...</p></li></ul>